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A special youth and space panel will be held at UNISPACE+50 in Vienna on 19 June, including astronaut Scott Kelly, the UN’s ‘Champion for Space’. The panel will provide a forum to discuss technical advancements and findings in space and new opportunities for society, focussing, as the title implies, on young people!

We asked several young Europeans (and a Canadian!) working at ESA for their perspective on the future and what they hope to see in coming years.

Aybike Demirsan
Hometown: Frankfurt am Main, Germany
Work: Young Graduate Trainee at ESA working on software for the Cluster mission 

Aybike Demirsan

Two years ago, I entered ESA’s Young Graduate Trainee programme with a position at the Agency’s ESOC mission control centre in Darmstadt, Germany. I am working on the Cluster mission, comprising four structurally identical spacecraft that fly in formation to measure the solar wind’s effects on Earth’s magnetosphere.

My job, thanks to my background in computer science, is to reengineer the mission’s monitoring tool, so that it would be easier for the flight control team to monitor the upcoming contacts between our spacecraft and the ground stations. The tool employs a simple visual timeline, with many more functionalities than before, to make our lives as spacecraft operations engineers and spacecraft controllers easier.

I also received training on every subsystem of the spacecraft and learned how to operate spacecraft and how to deal with anomalies, which has been a great journey.

However, it’s not only what we do that fascinates me, but also the way we do it. Never before have I worked with such a diverse crowd of people, and as well I have never before worked in such a peaceful, nourishing environment where knowledge is shared, help is always offered and there is belief and trust in others and yourself to do your job with your best effort. For space in the future, I think youth today can look forward to worldwide collaboration and to overcoming artificial human-created borders!

Artur Scholz
Hometown: Erlangen, Germany
Work: Spacecraft Operations Engineer at ESA working on the Cluster and JUICE missions 

Artur Scholz

For space in future, youth today should most look forward to work together openly, with a focus on sharing and collaboration.

The spirit of open source, which comes from the software world, should be applied to all areas of space exploration – because what we need to truly advance access to space is to allow everyone to get involved!

Dr Francesca Letizia
Hometown: Cagliari, Italy
Work: Space Debris Engineer at ESA working on assessing compliance with space debris mitigation guidelines

Francesca Letizia

There are three main aspects of future space activities that I find exciting. The first one is related to exploration: In the upcoming years, we will witness increasing efforts to send astronauts to Mars and, in general, beyond low Earth orbit. Several projects – like the Lunar Orbiing Platform – Gateway and Moon Village – are evaluating extended human presence in orbits much more distant from Earth than the current International Space Station. These initiatives could contribute to a deeper understanding of the limits of the human body (and mind) in space and how to handle these.

Another interesting field is the development of planet-hunter missions, such as NASA’s Kepler spacecraft now in orbit and the planned ESA Plato and Cheops missions. The goal of these spacecraft is to find planets outside our Solar System and, in particular, to identify planets with a habitable environment. The findings of these missions are incredibly fascinating as they shed light on where life could have developed outside of Earth.

Finally, in the future, space will be more and more an enabler of new technology and applications. This is already happening right now with navigation services such as GPS and could be even more exploited and integrated thanks to the improved accuracy offered by Galileo. Other opportunities are offered by the processing of satellite images in fields such as agriculture or monitoring of land and water use.

Adam Vigneron
Hometown: Wilcox, Saskatchewan, Canada
Work: Navigation Engineer, on contract from Telespazio VEGA Deutschland, at ESA’s Navigation Support Office

Adam Vigneron Credit: J. Martin

My work in the Navigation Support Office has given me a profound example of the way in which space technology is an integral part of our everyday life. The work I do now inspires me to dream of a future where the line between space and daily life continues to blur…

For fifty years, uncrewed spaceflight has been a one-way trip. Two related mission families, active debris removal (ADR) and on-orbit servicing (OOS), are looking to turn this trip on its head. Briefly, ADR involves the removal of dead satellites from useful orbits, while OOS includes the refuelling and repairing of satellites already in orbit.

After numerous stops and starts, rumblings are happening in all the right places. Technology demonstrations of advanced robotics are ongoing on the International Space Station, proving technologies for fuel transfer and battery replacement. It looks as though the world’s first ADR mission, e.Deorbit, will gain attention at next year’s ESA Ministerial Council. Discussions continue at UNCOPUOS, the UN body which allows countries to agree on standards and norms for the peaceful use of outer space. Industrial players around the world are jockeying for position as this market emerges. All the while, valuable orbits in LEO and GEO are slowly but steadily filling up with active satellites and debris alike.

ADR/OOS promise an economically viable revolution in space activities to which today’s globally-minded, engaged youth are well-suited. There is a lot of work to be done, but with determination, we can make these missions come to life and change the way we look at space itself by making in-space repair as everyday ordinary as satellite navigation is today.

Editor’s note

Find out more about the misisons and activities mentioned above:

Cluster mission operations

JUICE mission

Space Debris Office

Navigation Support Office

e.Deorbit/Active debris removal

On-orbit servicing

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Guest post by Ersilia Vaudo Scarpetta

Ersilia Vaudo Scarpetta has been working at the European Space Agency since 1991 and she is currently Chief Diversity Officer.

Ersilia Vaudo | Credits: Zoe Vincent/Wired Italy

Today at Unispace+50, the role of women in space has been placed front and centre, and rightly so.

The topic of diversity and inclusiveness (D&I) has been recently placed high on ESA’s corporate agenda. Through this initiative, ESA intends to enhance its wealth of diversity, and at the same time ensure that the values and the objectives pursued through D&I actions become an inherent feature of the Agency’s policies and business practices.

Last September, as part of this effort, ESA’s commitment toward diversity and inclusiveness was made visible, reinforced and underlined in a policy statement that you can read on ESA’s website. The Agency’s final aim is to create and ensure a modern, inclusive working environment where people value diversity in teams, take others’ perspectives into account and feel comfortable being themselves – regardless of gender, gender identity and expression, age or working experience, sexual orientation, physical or mental challenges, ethnicity or educational, religious or social background.

Actually, diversity is already a distinctive feature of ESA and is one of its greatest assets – same as for its international character. People from 22 European member states (plus Canada and Slovenia as Cooperating State and Associate State, respectively) – speaking more than 18 different languages – work together, discussing and solving problems every day by combining their different cultural backgrounds. It is that richness of diversity, in competences, skills and points of view that allows us to achieve results that could be impossible to reach on the effort of single nations. The Agency has put a renewed effort into striving to enhance the innovative perspectives brought in by a diverse and gender-balanced pool of talent.

Among the different activities undertaken to foster diversity and inclusiveness at ESA, a special focus has been put in ensuring that space jobs are increasingly attractive to women in ESA member states.

In fact, we observe that, although space is recognised as one of the most inspirational sectors in science and technology in Europe, and the number of girls in science, technology, engineering and maths (STEM) is growing in member states, applications from women to ESA are are only holding steady. In addition, if the situation in Europe is improving in terms of girls graduating in STEM fields, this is still a ‘boys’ club’.

Furthermore, in terms of perspectives, we see that the number of women decreases along the different steps of a STEM career. It becomes therefore clear that we need to challenge stereotypes, become more proactive in promoting space jobs and work for the right conditions for retaining and ensuring career perspectives to women.

ESA is part of a number of external networks with other international organisations to promote discussions on these issues, exchanging ideas as well on current measures and best practices. It is with this aim that ESA has established a network with member states on diversity and inclusiveness, is part of the ad-hoc EIROforum Working Group on Diversity, and has initiated a collaboration with the OECD on the topic of gender and stereotypes in science. ESA is also corporate member of Women in Aerospace Europe.

Ersilia Vaudo | Credits: Zoe Vincent/Wired Italy

With the Agency facing a significant retirement wave coming over the next 10-15 years, this moment really represents the perfect occasion to project the ‘ESA of the future’ and to start injecting more diversity into the workforce.

ESA already has a long-standing commitment to promoting gender diversity and equal opportunities. Focusing on, and strongly committing to, the involvement of women in STEM is more important today than ever in order to continue and expand ESA’s enduring value – and enhance it in the future from a Space 4.0 perspective. In fact, in the next decades we will be more and more in need of a creative and diverse pool of talent to address challenges of the future.

With this overarching objective in mind, the Agency is now working to achieve measurable goals in terms of female recruitment and representation. For example, in terms of new recruitments we will be aiming at a minimum 30% of new positions filled by women by 2019. In addition, efforts have been put in place to increase the proportion of women in leadership positions, which is at ESA around 10%.

Furthermore, since the Agency receives a gender-balanced number of applications at the young-graduate level while the number of women interested in permanent jobs drops to about 20%, ESA is opening the early-career scheme also to people in their 30s with some years of working experience.

Finally, the Chief Diversity Officer and many of ESA’s female professionals regularly engage in branding and outreach activities to inspire girls and young women across Europe to enter STEM disciplines, encouraging in particular careers in science, engineering and space.

Indeed, at ESA we are sure that diversity will help us strengthen innovation, lessen resistance to change, obtain a broader understanding of societal needs, boost motivation, inspire people and foster knowledge sharing. Spurred on by the UN’s Sustainable Development Goals (SDGs), and in particular SDGs that aims at equal opportunities for all women and girls, ESA has a major objective to inspire the young generation of girls to enter the STEM field and in particular to attract more women to the wealth of careers and jobs that space can offer.

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A tired but very happy Mars Express flight control team pulled shift through the night between 16 and 17 April, overseeing the successful reboot and recovery of ESA’s nearly 15-year-old Red Planet explorer following the installation of significant updates to the spacecraft’s operating system.

One online media channel, following the event via Twitter, reported: “The team behind the European Space Agency’s Mars Express were cock-a-hoop with delight last night after hitting the big red button to restart and install updates on the veteran orbiter.”

It’s true. We were!

Just like when your smartphone or tablet receives new software to improve its functionality and extend its life, Mars Express got an upgrade to enable it to keep flying despite the fact that several critical components (ring-laser gyros) are wearing out (see Mars Express V2.0 for details).

But unlike with your phone or tablet, this update was delivered across 144.6 million km of space.

There was a bit of tension in the Interplanetary Control Room at ESOC last night, especially between sending the reboot command at 19:15 CEST and waiting for the craft to restart and send a signal about an hour later.

Spacecraft operations engineers are naturally risk averse and prone to pessimism, and – rightly so – they hate just hanging around waiting for a possibly recalcitrant spacecraft to do what it’s been told.

But, if you followed @esaoperations via Twitter, you’ll know the expected signal came in around 20:15 CEST and the initial results were entirely good, which is to say, entirely as expected:

Receipt of the low-bitrate signal from #MarsExprsss is great news! This means the craft has rebooted. Now waiting for telemetry – onboard status info… #rday

— ESA Operations (@esaoperations) April 16, 2018

That happy feeling when your phone restarts! Initial #MarsExpress status looks good! It is running on the new software & its systems appear to be operating as expected #Rday

— ESA Operations (@esaoperations) April 16, 2018

The update from the team today confirms their initial reaction: the spacecraft is doing well and the newly updated software is working more or less as expected.

“Everything went according to plan with only minor issues,” says Spacecraft Operations Manager James Godfrey.

“Today, the team on shift is concentrating on reconfiguring the spacecraft into normal operating mode, testing functionalities and checking to see if anything fails to work with the new software.”

This testing and shakeout will continue for the next approximately 7 to 8 days, and the team expect to be able to switch the science instruments back on and return to routine observations by the end of April.

“Everyone at ESA did an excellent job in this entire upgrade effort,” says ESA Flight Director Michel Denis.

“It took a lot of work and coordination by the flight controllers, assisted by experts from flight dynamics, ground stations and software support as well as by our colleagues working on the Mars Express Science Operations team.”

“We have a spacecraft in excellent shape and promising many more years of exploration at Mars.”

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Editor’s note: ESA’s Space Debris team have sent in a final update on the reentry of Tiangong-1.

As we posted earlier, around once a year, ESA takes part in a joint tracking campaign run by the Inter Agency Space Debris Coordination Committee (IADC), which consists of experts from 13 space organisations such as NASA, Roscosmos, CNSA and European and other national agencies.

With the agreement of all members, Tiangong-1’s reentry was the mission selected for this year’s campaign.

During the now-completed campaign, participants pooled their predictions of the time window, as well as their respective tracking datasets obtained from radar and other sources, with the aim of cross-verifying, cross-analysing and improving the prediction accuracy for all members.

ESA has been acting as host and administrator for the campaign, as it has done for the about twenty previous IADC test campaigns since 1998.

Tiangong-1 seen at an altitude of about 161 km by the powerful TIRA research radar operated by the Fraunhofer Institute for High Frequency Physics and Radar Techniques (FHR) near Bonn, Germany. Image acquired on the morning of 1 April 2018, during one of the craft’s final orbits. Credit: Fraunhofer FHR

Besides the IADC campaign, ESA also had an operational role: Throughout the past days it supplied its own predictions to national alert and civil protection centres of Member States.

Confirmation of this morning’s Tinagong-1 reentry was published by the US military, who issued a press release today at around 04:00 CEST.

They stated that reentry had occurred over the southern Pacific Ocean at approximately 5:16 p.m. (PST), which was 02:16 CEST – this was well within ESA’s earlier reentry forecast window, which ran from 23:00 UTC on 1 April to 03:00 UTC on 2 April (01:00 CEST to 05:00 CEST on 2 April).

“According to our experience, their assessment is very reliable,” says Holger Krag, Head of ESA’s Space Debris Office.

“This corresponds to a geographic latitude of 13.6 degrees South and 164.3 degrees West – near American Samoa in the Pacific, near the international date Line.

“Both time and location are well within ESA’s last prediction window.”

Holger notes that, afterwards, at 04:05 UTC (06:05 CEST), had Tiangong-1 still been in orbit, it would have become visible to the Fraunhofer FHR institute’s TIRA radar, located near Bonn. In fact, the team working at TIRA reported that the spacecraft was no longer visible, giving additional confirmation that it had reentered.

Indeed, data supplied by many a number of ESA partners were crucial to enable the space debris team to conduct their work. “We’d certainly like to thank all our partners who supported ESA throughout this campaign,” says Holger.

China’s CMSA manned space agency also made a public statement.

It’s interesting to note, from a European perspective, how limited our capabilities still are after all. Most of the data on space objects that ESA receives today comes from non-European sources.

Europe’s missing information

Commands for a debris avoidance manoeuvre being sent to ESA’s Swarm-B on 25 January 2017. Credit: ESA

“This illustrates again the dependence that Europe has on non-European sources of information to properly and accurately manage space traffic, detect reentries such as Tiangong-1 and track space debris that remains in orbit – which routinely threatens ESA, European and other national civil, meteorological, scientific, telecomm and navigation satellites,” says Holger.

The US military routinely warns ESA when one of the Agency’s satellites may be at risk for collision with a piece of space debris, an event that is happening with increasing frequency (see Anatomy of a debris incident).

Holger points out that Europe also lacks the means to independently confirm reentries the size of Tiangong-1, which occur almost weekly, by using, for example, an infrared tracking payload mounted on a geostationary satellite.

Space weather, too

He also mentions that, three days ago, solar-generated space weather gave us a surprise, when the Sun’s activity spontaneously dropped compared to what the team expected.

“This delayed the Tiangong-1 reentry by about half a day.”

Concept for ESA’s future space weather monitoring mission at the Sun. Credit: ESA/A. Baker, CC BY-SA 3.0 IGO

Earlier this year, ESA in cooperation with European industry began a multi-year study to examine a new mission (see “Where no mission has gone before“) that would continuously observe our Sun and provide crucial data that will help us improve our forecasts of solar activity and its effects on spacecraft, satellites in orbit and critical infrastructure on ground such as power grids and oil pipelines.

Since 2009, ESA has been developing software, technologies and precursor systems to test a fully European network of radars, telescopes and other detectors that would provide independent data on the risks from spaceflight.

Concept for ESA’s future space debris surveillance system employing ground-based optical, radar and laser technology as well as in-orbit survey instruments. Credit: ESA/Alan Baker, CC BY-SA 3.0 IGO

“Today, everyone in Europe relies on the US military for space debris orbit data – we lack the radar network and other detectors needed to perform independent tracking and monitoring of objects in space,” says Holger.

“This is needed to allow meaningful European participation in the global efforts for space safety.”

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The US air force has confirmed the reentry of the Tiangong-1 spacecraft at about 02:16 CEST this morning over the southern Pacific Ocean. The location of the reentry was, by chance, not too far from the so-called South Pacific Ocean Unpopulated Area. The SPOUA has long been used by many space agencies including ESA, to dispose of end-of-life spacecraft through controlled reentries. 

The air force wrote:

The JFSCC used the Space Surveillance Network sensors and their orbital analysis system to confirm Tiangong-1’s reentry, and to refine its prediction and ultimately provide more fidelity as the reentry time approached. This information is publicly-available on USSTRATCOM’s website www.Space-Track.org. The JFSCC also confirmed reentry through coordination with counterparts in Australia, Canada, France, Germany, Italy, Japan, South Korea, and the United Kingdom.

JFSCC tracks Tiangong-1’s reentry over the Pacific Ocean

VANDENBERG AIR FORCE BASE, Calif. — U.S. Strategic Command’s (USSTRATCOM) Joint Force Space Component Command (JFSCC), through the Joint Space Operations Center (JSpOC), confirmed Tiangong-1 reentered the Earth’s atmosphere over the southern Pacific Ocean at approximately 5:16 p.m. (PST) April 1, 2018.


 

Read full report via:

http://www.vandenberg.af.mil/News/Article-Display/Article/1481734/jfscc-tracks-tiangong-1s-reentry-over-the-pacific-ocean/

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Main Control Room at ESA’s European Space Operations Centre, Darmstadt, Germany. Credit: ESA/P. Shlyaev

With the reentry of Tiangong-1 now forecast to happen within a few hours, ESA’s formal role in the tracking campaign is winding down.

To recall, here’s what’s been happening.

Each year, about 100 tonnes of defunct satellites, uncontrolled spacecraft, spent upper stages and discarded items like instrument covers are dragged down by Earth’s upper atmosphere, ending their lives in flaming arcs across the sky.

While still in orbit, these and many other objects are tracked by a US military radar network, which shares the data with ESA, since Europe has no such capability of its own.

IADC campaign

Around once a year, ESA takes part in a joint tracking campaign run by the Inter Agency Space Debris Coordination Committee, which consists of experts from 13 space organisations such as NASA, Roscosmos, CNSA and European and other national agencies.

With the agreement of all members, Tiangong-1’s reentry was the mission selected for this year’s campaign.

During the campaign, participants have been pooling their predictions of the time window, as well as their respective tracking datasets obtained from radar and other sources, with the aim of cross-verifying, cross-analysing and improving the prediction accuracy for all members.

ESA has been acting as host and administrator for the campaign, as it has done for the twenty previous IADC test campaigns since 1998. A special case for ESA was the campaign in 2013 during the uncontrolled reentry of ESA’s own GOCE satellite.

The China Manned Spaceflight organisation have been providing their own updates on reentry, and additional Tiangong-1 orbit information is here.

ESA’s reentry expertise

In addition to IADC campaigns, it is the task of ESA’s Space Debris team to generate its own independent predictions to ESA Member States and partner civil authorities around the globe.

ESA reentry expertise - YouTube

The team mix in additional tracking information gleaned from European sources, such as Germany’s Fraunhofer research radar near Bonn or telescopes and other detectors run by a mix of institutional and private researchers, to generate reentry forecasts – a challenging and imprecise art.

We’ve been posting ESA’s reentry forecasts regularly here in the blog, and sharing the link via social media.

Getting close

In just a few hours, we’ll be well within the uncertainty window associated with this reentry, and we don’t expect any more forecast updates with any higher accuracy. In other words, we’re at the limit of what we can forecast.

Just over an hour ago, ESA’s space debris team provided their final estimate for reentry, forecasting a window of about four hours between 23:00 UTC on 1 April to 03:00 UTC on 2 April (01:00 CEST on 2 April to 05:00 CEST on 2 April).

Final Tiangong-1 reentry window forecast for 18:00 CEST 1 April Credit: ESA

Final Tiangong-1 altitude decay forecast as of 18:00 CEST, 1 April Credit: ESA

“With our current understanding of the dynamics of the upper atmosphere and Europe’s limited sensors, we are not able to make very precise predictions,” says Holger Krag, head of ESA’s Space Debris Office.

Holger says that there will always be an uncertainty of a few hours in all predictions, and that even just a day or so before any reentry, like now, the uncertainty window can be very large.

“The high speeds of returning satellites mean they can travel thousands of kilometres during that time window, and that makes it very hard to predict a precise location of reentry.”

Spotting reentry

It is likely that the pending reentry of Tiangong-1 will occur over water, probably unseen by anyone (although possibly detected by radar or other sensors).

Tiangong-1 seen at an altitude of about 161 km by the powerful TIRA research radar operated by the Fraunhofer Institute for High Frequency Physics and Radar Techniques (FHR) near Bonn, Germany. Image acquired on the morning of 1 April 2018, during one of the craft’s final orbits. Credit: Fraunhofer FHR

Our planet is a big place, mostly covered by water, and if any pieces survive the fiery reentry, these are unlikely to be found by anyone, sinking instead to the bottom of some ocean, or landing far from human habitation.

If you do witness the event, we’d certainly like to see any images you get.

These will help ESA’s debris team conduct their post-reentry analysis, and improve models and forecasts for future.

We need the time, your location (GPS coordinates fine) and – ideally – the direction in which you were facing when you saw any arc across the sky.

You can share your photos via Twitter (just tag @esaoperations), or mail them to esoc.communication@esa.int. We’ll reply for a confirmation and any follow-up.

In the unlikely case that you find a piece of debris on ground, leave it alone and inform your local authorities.

Our final word comes from last week’s web article, which closed with an observation worth repeating:

Since 2009, ESA has been developing software, technologies and precursor systems to test a fully European network that would provide independent data on the risks from spaceflight.

“Today, everyone in Europe relies on the US military for space debris orbit data – we lack the radar network and other detectors needed to perform independent tracking and monitoring of objects in space,” says Holger Krag.

“This is needed to allow meaningful European participation in the global efforts for space safety.”

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Every week, on average, a substantial, inert satellite drops into our atmosphere and burns up. Monitoring these reentries and warning European civil authorities has become routine work for ESA’s space debris experts.

ESA reentry expertise - YouTube

Each year, about 100 tonnes of defunct satellites, uncontrolled spacecraft, spent upper stages and discarded items like instrument covers are dragged down by Earth’s upper atmosphere, ending their lives in flaming arcs across the sky.

Some of these objects are big and chunky, and pieces of them survive the fiery reentry to reach the surface. Our planet, however, is a big place, mostly covered by water, and much of what falls down is never seen by anyone, sinking to the bottom of some ocean, or landing far from human habitation.

While still in orbit, these and many other objects are tracked by a US military radar network, which shares the data with ESA, since Europe has no such capability of its own.It’s the task of ESA’s Space Debris team to look at these data and issue updates to ESA Member States and partner civil authorities around the globe.

Access full text via ESA web.

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Today’s blog post was sent in by Stijn Lemmens, an analyst working in ESA’s Space Debris Office at ESOC in Darmstadt, Germany.

We are now within days of the projected Tiangong-1 reentry. One question that ESA’s space debris team has been receiving frequently is, why is the actual reentry date and time remain so uncertain – even as the predicted time window has been shrinking steadily (and is now considerably smaller) since our original estimates were posted here back in January.

Animation of successive Tiangong-1 radar images acquired by the Tracking and Imaging Radar (TIRA) operated by Fraunhofer FHR, Wachtberg (near Bonn), Germany. Actual images shown at left together with an animated computer model to illustrate motion of the craft. TIRA data are being used in the ESA-hosted reentry tracking campaignMore details via the FHR website

As can be seen in our regularly updated time-window plots, the uncertainty on the predicted reentry epoch (time and date) – in other words, on the remaining orbital lifetime – has been running at about plus or minus 20%, and the actual predicted reentry date has been subject to quite some variability.

This variability is largely driven by inaccuracy in forecasting the density of the lower layers of the thermosphere. This is the upper level of Earth’s atmosphere, producing the drag which is responsible for the decay of the orbit, which in turn depends on a number of atmospheric models and actual space weather activity.

These atmospheric models are applied to many aspects of spaceflight.

They provide a fast algorithm to calculate the temperatures, densities and chemical composition of the atmosphere at any given time and position around the Earth. These values are indispensable for the orbit-determination and orbit-prediction aspects of any mission. The models are based on the ‘energy balance’ physics of the atmosphere, just like climate models for Earth science, and are calibrated based on satellite measurements to provide averaged solutions.

Four models are commonly used for spaceflight. These are known as:

  1. NRLMSIS00
  2. DTM-2013
  3. GOST-2004
  4. JB2008

In order for these models to do their orbital determination and prediction jobs, they require so-called ‘proxies’ to describe how space weather affects spaceflight, e.g. how much energy the Sun is sending to Earth and how these radiation and particle streams interact with the near-Earth environment.

Commonly used proxies include the energy flux received in the radio spectrum (the ‘F10.7 Index’), the Sun spot number (SSN), and current level of disturbance in Earth’s geomagnetic field (‘Ap Index’). More detailed information can be found via the Space Debris Office technical website – see Section 4. The variations in space-weather proxies result in large changes in the predicted reentry time.

Foreseeing the future

Statistical and machine learning techniques can be used to make such forecasts on the time scale of days to years, but in reality, it has proven to be difficult to capture this in predictive models. Forecasts on shorter timescales, days to hours, tend to be a little better but require essentially a large dose of supercomputing and human ingenuity.

Furthermore, when it comes to spaceflight in the lower thermosphere, dedicated satellite observations that can be used to calibrate the reentry models (coming from missions such as ESA’s low-orbiting GOCE satellite) are rare and hence all models need to extrapolate to a large degree.

The sum of these effects – along with the core fact that even decaying objects in orbit are still in motion around Earth at upwards of 7.8 km per second – is what makes uncontrolled reentries so difficult to forecast, and imply that even seven hours prior to reentry, a given prediction can still have an uncertainty on the final impact point of one full revolution around the Earth.

Breaking up is easy to do but hard to predict

Predictions closer to reentry are possible, but only when the object is observed, which cannot be guaranteed as the object would need to pass over a sensor – like a telescope or radar. Even assuming perfect knowledge, any potential fragments generated following reentry breakup would spread out somewhat randomly over a ground track on average hundreds of kilometres long and a few tens of kilometres wide (which is why the risk of hitting a person on the ground is very, very low).

The interplay between the atmosphere models and other effects such as the object’s relative facing position, or attitude (which increases or decreases its surface area exposed to the atmosphere), cannot be unambiguously decoupled based on trajectory data alone (see more details, for example, here).

In a nutshell: a drag coefficient as derived from space surveillance for Tiangong-1 is the result of averaging the observed decay behaviour of the space station over days against an averaged atmosphere model. It is not not an instantaneous measurement. Note also that radar image data (see animation above) have so far confirmed a continuing and increasing rotation rate for Tiangong-1.

Direct observations of the attitude of re-entering objects from the ground are complicated by the fact that continuous observation times are limited to generally ten minutes or less (before the object orbits out of sight below the horizon).

Hence lower rotation periods can only be extrapolated at best. Sparse sensor coverage generally leads to many gaps, which need to be covered by predicting the attitude evolution during the object’s passage from one sensor to another, which again requires a significant amount of detailed knowledge of the object, especially when the atmosphere has a significant effect, as it does during re-entries.

Data sources: radars, ‘scopes and lasers

A standard ‘triumvirate’ of sensors is used to tackle this task for targets in a variety of orbits: radar, optical telescopes and lasers; all have their benefits and drawbacks with regard to attitude determination. Radars can provide frequent coverage but the attitude needs to be reconstructed from the Doppler information where the response is difficult to interpret – this applies to both Radar Cross Section (RCS) and Inverse Synthetic Aperture (ISAR) techniques.

Optical telescopes unfortunately require propitious illumination conditions on the target, but are generally suited for establishing the long-term trending of the rotational motion. And lasers require either high power or reflective surfaces on the target, but when combined with accurate positional knowledge and surface information these can enable the reconstruction of the full attitude motion with a minimum of ambiguity.

The best way of reconstructing shifting attitude is to combine data from all three sensor types to resolve the individual ambiguity. ESA is pioneering this field of ‘fused attitude surveillance’ as well as further developing sensor capabilities. An introduction to the subject is available here.

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FAQ on Tiangong-1 reentry

FAQ prepared and updated by the Space Debris Office, ESA/ESOC, Darmstadt, Germany.

Read these FAQ in German

Preguntas frecuentes sobre la reentrada de Tiangong-1

Tiangong-1 (天宫一号, Heavenly Palace 1) is China’s first space station and an experimental space laboratory. Its major goal was to test and master technologies related to orbital rendezvous and docking. It is identified by its UN COSPAR ID 2011-053A. It was launched on 30 September 2011 at 03:16:03.507 UTC by a Long March 2F/G rocket from the Jiuquan Satellite Launch Centre in the Gobi desert, Inner Mongolia, China. One uncrewed and two crewed missions, executed by the Shenzhou (神舟, Devine Craft) spacecraft, took place during its operational lifetime.

Note: The latest, updated reentry time window forecast will be posted in the homepage of this blog. Read more via ESA joins reentry campaign.

Q. What’s happening?

The Tiangong-1 space station will reenter Earth’s atmosphere and substantially burn up in the March–April 2018 timeframe.

As of mid-January 2018, the spacecraft was at about 280 km altitude in an orbit that will inevitably decay; it will mostly burn up due to the extreme heat generated by its high-speed passage through the atmosphere (some spacecraft, like Soyuz capsules, are designed to withstand reentry).

Following launch in 2011, the Tiangong-1 orbit began steadily decaying due to the faint, yet not-zero, atmospheric drag present even at 300 or 400 km altitude. This affects all satellites and spacecraft in low-Earth orbit, like the International Space Station (ISS), for example.

Tiangong-1 space station. Credit: CMSE/China Manned Space Engineering Office

As a result, such craft must conduct regular ‘reboost manoeuvres’ to maintain their orbit – typically, ground controllers command the craft’s engines or thrusters to fire for a certain amount of time, speeding it up so that it gains altitude.

During its operational life from launch through to December 2015, regular orbital maintenance manoeuvres were executed by Tiangong-1 in order to maintain an operational altitude of between 330 and 390 km above the Earth’s surface.

Q. What was the original disposal plan?

Initially, a ‘controlled reentry’ was planned for the spacecraft at the end of its life.

This means that ground controllers would have commanded the engines to fire, slowing the craft by a significant amount so that it would fall toward the surface. Firing the engines would have been done at a specific moment so that it would reenter the atmosphere and substantially burn up over a large, unpopulated region of the South Pacific ocean. Any surviving pieces would fall into the ocean, far from any populated areas. This is precisely what ESA did, for example, for the Agency’s series of five ATV cargo spacecraft between 2008 and 2015.

However, in March 2016 the Tiangong-1 space station ceased functioning but maintained its structural integrity. In so far as can be fully confirmed, ground teams lost control with the craft, and it can no longer be commanded to fire its engines. It is, therefore, expected to make an ‘uncontrolled reentry.’ 

Q: How big is Tiangong-1? What shape is it?

The spacecraft’s 10.4 m-long main body is made up of two cylinders of approximately equal length: a service module and an experiment module. The thinner service module provides power and orbit control capabilities for the station. It has two solar panels, each approximately 3 x 7 m in size. The thicker experimental module comprises an enclosed front conical section, which include a docking port, a cylindrical section, and a rear conical section. The experimental module is habitable.

This vivid image shows China’s space station Tiangong-1 – the name means ‘heavenly palace’ – and was captured by French astrophotographer Alain Figer on 27 November 2017. It was taken from a ski area in the Hautes-Alpes region of southeast France as the station passed overhead near dusk. The station is seen at lower right as a white streak, resulting from the exposure of several seconds, just above the summit of the snowy peak of Eyssina (2837 m altitude). Credit: A. Figer. Used by permission.

The overall mass of the spacecraft was reported to have been approximately 8.5 tonnes including fuel at launch. Given that the space station exceeded its originally planned operational lifetime of two years and continued operating successfully for two more years after that, a considerable amount of fuel must have been consumed to sustain the orbit and the habitable environment conditions inside.

This means that a significantly lower mass on reentry is likely, comparable to the mass of defunct satellites that make uncontrolled reentries typically a couple times per month.

Q. To date, who’s done or is doing what?  

China notified the United Nations Office for Outer Space Affairs (UNOOSA) of the upcoming re-entry and committed to enhanced monitoring and forecasting of the orbital decay, including requesting an international joint monitoring and information dissemination campaign under the framework of the Inter-Agency Space Debris Coordination Committee (IADC).

IADC comprises space debris and other experts from 13 space agencies/organisations, including NASA, ESA, European national space agencies, JAXA, ISRO, KARI, Roscosmos and the China National Space Administration.

IADC members will use this event to conduct their annual reentry test campaign, during which participants will pool their predictions of the time window, as well as their respective tracking datasets obtained from radar and other sources. The aim is to cross-verify, cross-analyse and improve the prediction accuracy for all members.

ESA is acting as host and administrator for the campaign, as it has done for the twenty previous IADC test campaigns since 1998. A special case for ESA was the campaign in 2013 during the uncontrolled reentry of ESA’s own GOCE satellite.

Regular updates are being provided via the website of the China Manned Space Agency in both Chinese and English.

As of January 2018, the mean altitude of the space station is 280 km. The further decay, and hence re-entry, is assumed to be uncontrolled in the sense of orbit maintenance. This has, however, not been unambiguously confirmed by the Chinese authorities. It has however been reported that the attitude, i.e. the orientation, of Tiangong-1 is stabilised.

Q. Over which parts of Earth will it burn up?

Due to the orbital inclination of the Tiangong-1, approximately 42.8 degrees, and the likely uncontrolled nature of the reentry, the final impact point can be anywhere on Earth between 42.8 degrees North and 42.8 degrees South in latitude.

Map showing the area between 42.8 degrees North and 42.8 degrees South latitude (in green), over which Tiangong-1 could reenter. Graph at left shows population density. Credit: ESA CC BY-SA IGO 3.0

As you can see in the chart at right in the map above, the re-entry location itself is not uniformly distributed. Due to the geometry of the craft’s circular orbit, the probability of reentry happening at the maximum (42.8 degrees N) and minimum (42.8 degrees S) latitude are higher than at the equator.

Why is this?

Because of the low eccentricity and non-polar inclination of the orbit (in other words, because the orbit of the space station around the Earth is circular and at an angle with respect to the equator), the space station spends more time near the edges of the band then it spends crossing the equatorial region of Earth. This leads to a higher likelihood of reentry occurring near the edges of the latitude band, i.e., the top and bottom of the band in the map above.

Q. Will anyone know the precise location and time of reentry in advance?

Only from one day before the actual reentry will it become possible to roughly predict which ground tracks, and hence which regions on Earth, might witness the reentry.

But even then, an impact location prediction on the order kilometres is, for an uncontrolled reentry, beyond current technical capabilities due to complexities of modelling the atmosphere, the dynamics of the reentering object and limitations in observing the spacecraft.

In general, the uncertainty associated with an uncontrolled reentry prediction is on the order of 20% of the remaining orbital lifetime. Practically, this means that even 7 hours before the actual reentry, the uncertainty on the break-up location is a full orbital revolution – meaning plus or minus thousands of km!

The latest reentry forecast will be posted here.

If the spacecraft does have a functioning attitude control system now, this could stop working under the higher dynamic pressure loads (due to falling lower into the atmosphere) closer to reentry and the uncertainty in the final reentry time window could rise (this was the case, for example, with ESA’s GOCE reentry).

Q. Once it reenters and breaks up, what is the risk that any pieces reach ground?

Tiangong-1 is a large spacecraft comparable in size and mass to other, frequently used space stations and cargo vessels such as ESA’s ATV, the Japanese HTV, Russian Progress and American Dragon or Cygnus.

From monitoring the controlled reentries of those types of spacecraft, it can be surmised that Tiangong-1 will break up during its atmospheric re-entry and that some parts will survive the process and reach the surface of Earth.

Video of ESA’s ATV 1 breaking up during its controlled reentry in September 2008

ATV-1 reentry - YouTube

Given the uncontrolled nature of this reentry event, the zone over which fragments might fall stretches over a curved ellipsoid that is thousands of kilometres in length and tens of kilometres wide. While a wide area could be affected, it is important to point out that a large part of the Earth is covered by water or is uninhabited.

Hence the personal probability of being hit by a piece of debris from the Tiangong-1 is actually 10 million times smaller than the yearly chance of being hit by lightning.

In the history of spaceflight, no casualties due to falling space debris have ever been confirmed.

Q. How does Tiangong-1 reentry compare to the reentries of similar-size craft in the past?

With its 8.5 metric tonnes of (initial) mass, Tiangong-1 is definitely not the largest uncontrolled reentry in spaceflight history. That would be Skylab with 74 metric tonnes.

Tiangong-1 falls within the category of modern space freighters (crewed and uncrewed) such as the already mentioned ATV (12 t), Japan’s HTV (10 t), Russia’s Progress (7 t) and Soyuz (7 t), the US Dragon (7 t) or Cygnus (5 t) and the Chinese Tianzhou (13 t). These masses are for the loaded craft; in the table below, they are shown at reentry.

Tiangong-1-class reentries Credit: ESA CC BY-SA 3.0 IGO Note: Shuttle Colombia (STS-107), with a mass of 82 t, unexpectedly broke up during a controlled reentry on 1 Feb 2003, leading to the loss of vehicle and crew.

Q. How will ESA share news or updates on the reentry?

In addition to news posted here in the blog, ESA will regularly update authorities in ESA Member States with detailed information on the reentry, as it does during all such events.

Q. What is ESA doing to tackle the problem of space debris?

ESA is leading the effort to tackle the problems of space debris by:

  • Monitoring and tracking objects in space
    By the end of the 2009-2020 period, ESA’s Space Situational Awareness (SSA) Programme will have overseen an investment of €200 million aiming to develop Europe-wide warning systems for space weather, near-Earth objects (such as asteroids) and debris objects left in orbit by human activities. Within SSA, ESA is developing and demonstrating the technologies needed to find and track debris and alert satellite operators – who control our vital weather, navigation, telecommunication and science research satellites – when evasive action may be necessary.
  • Developing technologies to mitigate and remediate space debris
    ESA’s Clean Space office launched the CleanSat project to support European Industry in developing technologies for spacecraft in low-Earth orbit that will then be fully compliant with debris-mitigation regulations. CleanSat covers four technology areas:1. Passivation: Explosions of satellites are a major source of debris. Passivation reduces the likelihood of a satellite exploding in the future by deactivating its power systems and batteries and venting any leftover propellant.2. Design for demise: Many spacecraft reenter the atmosphere. By using materials and designs that are likely to burn up entirely, the engineers are reducing the chances that pieces are left to hit the ground.3. Deorbiting systems: International debris guidelines require satellites to remove themselves from low-Earth orbit within 25 years of their end of life. ESA is carrying out studies to develop technologies that will ease the deorbiting at the end of life without affecting mission efficiency (examples include compact solid robot thrusters for deorbiting and ‘terminator sails’ that could be unfurled to increase air drag and hasten reentry).4. Design for servicing: This involves incorporating standard features onto future satellites, such as grips and handles, that will enable robotic servicing missions to capture satellites for removal, repair or refuelling.

While the first action to tackle the challenge of space debris is to stop producing further debris, it is also important to remove the largest items of debris currently in heavily-trafficked orbits, as a preventative measure to reduce the likelihood of future explosions or collisions.

Space debris - efforts to clean up space - YouTube

ESA’s Clean Space office is working to prepare the first ‘active debris removal’ (ADR) mission, called e.Deorbit. The objective of the mission is to use a custom satellite – the chaser – to capture a heavy, ESA-owned derelict satellite and remove it from an altitude of 800-1000 km and a near-polar orbital trajectory. The mission will be also an opportunity to demonstrate technologies needed for target characterisation, disposal methods and capture mechanisms – three technology areas of high interest to ESA and European industry for future space servicing vehicles.

Q. What specific technologies will help avoid future reentries such as this?

While not a specific technology, the main way for any spacecraft operator to avoid reentries such as this is to ensure that their missions are fully capable of conducting controlled, completely destructive reentries at the end of life. The specific technological approach taken depends on the mass of the spacecraft in question:

  • For satellites up to 1-2 tonnes: Technologies which will enhance ‘design for demise’ during reentry in the atmosphere. By using materials that are likely to burn up entirely during reentry and designs that will encourage complete breakup at an early point in the reentry process, already in the manufacturing phase engineers can reduce the chances that any pieces survive reentry to reach the surface.
  • For larger satellites: Efficient controlled deorbiting systems are needed. ESA is conducting studies to develop technologies that will ease deorbiting at the end of life without affecting overall mission efficiency, such as improved pressure gauges to maintain an accurate measure of the propellant remaining in a spacecraft’s fuel tank.

Access more information Clean Space and on the technologies under development within the CleanSat project via ESA’s CleanSpace blog.

More information

Media and press seeking more information can contact the ESA Communication team as follows:

esoc.communication@esa.int

ESA/ESOC Communication Office +49 6151 90 2516

Need more information on space debris?

ESA Space Debris Office

ESA Clean Space Office

ESA media relations website

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Latest reentry forecast provided by ESA’s Space Debris Office, ESOC, Darmstadt, Germany.

Update 26 March 2018

The current estimated reentry window remains between 30 March and 2 April; this is highly variable. 

Note: Read our updated FAQ in English Hier lesen Sie dieses FAQ in deutscher Sprache Preguntas frecuentes sobre la reentrada de Tiangong-1

Reentry will take place anywhere between 43ºN and 43ºS (see map here). Areas above or below these latitudes can be excluded. At no time will a precise time/location prediction from ESA be possible. This forecast was updated approximately weekly through to mid-March, and is now being updated every 1~2 days.

Tiangong-1 reentry window forecast as of 26 March Credit: ESA

Tiangong-1 altitude decay forecast as of 26 March Credit: ESA

Need more information on space debris?

ESA Space Debris Office

ESA Clean Space Office

ESA media relations website

Space for media

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